Typically, provisional components are designed to be reused, and have been known to be made out of various sturdy, reusable materials, such as stainless steel, cobalt chromium-molybdenum alloy, titanium or titanium alloy, aluminum (including anodized or Teflon coated aluminum), Delrin polyacetal, Celcon polyacetal copolymer, Ultraform polyacetal copolymer, polysulfone, and Ultem polyetherimide, as well as possible other similar reusable materials.
Although provisional components are not implanted, they must still be sterilized for surgical use since provisional components are used in surgery. Although provisional components could initially be provided presterilized, they are usually supplied nonsterile. If provided nonsterile, they must be sterilized before they are used. In addition, all provisional components must be resterilized before each additional surgical use. Typically, nonsterile provisional components are steam sterilized in an autoclave. Polyformaldehyde resins, such as polyacetals or polyacetal copolymers, have a somewhat limited life expectancy when subjected to repeated steam sterilization. However, polyacetal parts have been shown to withstand approximately 50 autoclaving or steam sterilization cycles. It is recommended that when the surface of such items becomes chalky, the item should be replaced.
There are three main types of sterilization procedures: gamma irradiation; steam sterilization; and ethylene oxide (EO) sterilization.
Gamma irradiation is used to produce a sterile product by exposing a product to radiation emitted by radioactive decay, and as such, is only available from a limited number of vendors that provide this process. Thus, this process is a commercially available process, and is not available in health care facilities, such as hospitals. This process can be applied to products through certain types of packaging materials, and as such, is an effective way of providing presterilized packaged products to the customer. Heat or high temperatures are not generated with this procedure.
Steam sterilization is used to produce a sterile product by direct contact of all surfaces of the device or instrument with steam and then revaporization of the water condensate to produce a sterile, dry product. The steam is produced by heating water above its boiling point. When steam contacts the device or instrument, a water condensate is left on the device. A drying phase is utilized to revaporize the condensate and dry the device or instrument. The vapor is removed from the steam sterilizer during this drying phase.
There are different methods of steam sterilization, such as gravity displacement and high vacuum, prevacuum, or pulsating vacuum. These steam sterilization procedures are typically conducted at temperatures of about 250.degree. to 270.degree. F. in a chamber often referred to as an autoclave. It is noted that sometimes a variation of the steam sterilization procedure is utilized by using a gravity displacement sterilizer when there is insufficient time to sterilize by the preferred wrapped or container method. This is sometimes referred to as "flash" sterilization, and is not typically a preferred method, except as an emergency procedure. Steam sterilizers or autoclaves are typically available in health care facilities, such as hospitals.
Ethylene oxide (EO) sterilization is used to produce a sterile product by exposing a product to ethylene oxide gas. This procedure is typically carried out at lower temperatures than steam sterilization. For example, the temperature of the sterilization phase for EO sterilization is generally 120.degree. to 145.degree. F. for a warm cycle or 85.degree. to 100.degree. F. for a cold cycle. However, the lower the temperature at which an item is sterilized, the longer it must be submitted to EO gas. EO sterilization is typically used for products which will not tolerate the high temperatures and/or moisture associated with steam sterilization. EO sterilization produces toxic residuals which dissipate upon adequate aeration. Thus, when using EO sterilization, an appropriate and effective exposure time to the EO gas and appropriate aeration time must be determined. Many medical materials and/or devices have not had appropriate tests for EO residue levels or sterility validation conducted on them. Such tests must be conducted before EO sterilization can be recommended for use on new, previously untested materials. It is noted that very few studies have been done on a potential buildup of EO residuals on repeated sterilization. Thus, repeated sterilization on a given product, more typically utilizes steam sterilization. Typically, polyethylene-containing implants are EO sterilized because the temperatures of steam sterilization can adversely affect the polyethylene components' dimensional stability. However, implants are not typically repeatedly sterilized. EO sterilizers are also typically available at health care facilities, such as hospitals.
It is noted that metal implants having a thin poly methyl methacrylate (PMMA) coating (such as disclosed in U.S. Pat. Nos. 4,491,987; 4,336,618; and 4,281,420) can be steam sterilized, which slightly softens the coating. However, the metal base of the implant enables the device to maintain the integrity of its shape and structure. Such PMMA coated implants could also be EO sterilized.
In addition, it is known to provide single use implants, such as distal centralizers (which are used to center the distal tip of a femoral hip stem) made from polymethyl methacrylate. These implants are not to be resterilized by steam sterilization, as such resterilization could destroy the structural integrity of the implant; however, they may be resterilized by ethylene oxide.